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Some black holes emit jets that are rapidly circling the poles of what appears to be a sphere at the center of the black hole, cf. Fig. 1.

Is there really a sphere here and how far (relative to the event horizon) are people seeing these jets start?

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So far there are no observations of a black hole with anywhere near enough resolution to resolve this. The black sphere is called the event horizon and represents the point where, because of the huge deformations to spacetime and its causal structure, not even light could escape. This is in principle observable (though only the Milky Way's central black hole is close enough to resolve it); see e.g. this answer.

The jets, on the other hand, have mostly been observed when Earth happens to lie in their line of sight - inside the jet, and luckily quite far away! Some jets have indeed been observed in noncollinear geometries, such as the one in M87, but we do not have the resolving power, at those distances, to observe the jet's launching region. For many black holes closer in - like the central black hole in the Milky Way - we do have plenty of indirect evidence that jets exist, but it's hard to observe them directly.

(Thanks to kleingordon for the correction.)

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  • $\begingroup$ "Of all the gas that falls toward the black hole, 99 percent gets spewed back out into space." Started thinking about this after reading: ca.news.yahoo.com/…Chandra X-Ray Observatory $\endgroup$ – AnimatedPhysics Sep 3 '13 at 0:15
  • $\begingroup$ Yes, this made several science headlines recently. Note that the observations are a study of the spectral properties of what (for Chandra) is essentially a point source. We measure weak emission at the wavelengths where we expect hot gas, and therefore we infer, indirectly, that there is little gas in the regions where it would be hot. $\endgroup$ – Emilio Pisanty Sep 3 '13 at 0:24
  • $\begingroup$ Off-axis jets have certainly been detected: the one emanating from M87 is among the most famous (en.wikipedia.org/wiki/Messier_87). But you're right that the we can't resolve the location where the jet is launched. $\endgroup$ – kleingordon Sep 3 '13 at 1:26
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    $\begingroup$ And it turns out the observations are more impressive than I realized. The wikipedia article links to a paper from 2012 in Science in which radio interferometry was used to probe the jet-launching region of M87. $\endgroup$ – kleingordon Sep 3 '13 at 1:31
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    $\begingroup$ Thank you for pointing this out: "We report radio interferometry observations, at a wavelength of 1.3 millimeters, of the elliptical galaxy M87 that spatially resolve the base of the jet in this source. The derived size of 5.5 ± 0.4 Schwarzschild radii is significantly smaller than the innermost edge of a retrograde accretion disk, suggesting that the M87 jet is powered by an accretion disk in a prograde orbit around a spinning black hole." http://www.sciencemag.org/content/338/6105/355 $\endgroup$ – AnimatedPhysics Sep 3 '13 at 18:00

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